EXTREMAL PROBLEMS

These transparencies were used for the second lecture in a series

of two lectures (the rst given by Noam Elkies) given at M.I.T.

in January, 2000, and are based on a book in preparation. They

are available at

www-math.mit.edu/rstan/trans.html#chess

Construction tasks.

Most number of moves by the eightWhite

ocers (with no Black units on the board)

M. Bezzel, 1849

Z Z Z Z

Z S Z Z

Z M Z Z

Z Z Z S

Z ABM Z

ZQZ Z Z

Z J Z Z

Z Z Z Z

One hundred moves by eight White pieces.

Proved by E. Landau in 1899 to be the maximum possi-

ble.

1

Kling (1849) asked: Can the eight White ocers control

(guard) every square, occupied or not?

Can only be done with bishops of the same color (unique

up to symmetry).

Kling, 1849

RZ Z Z Z

Z Z Z Z

ZBZ L Z

Z ZNZ Z

Z ZNZ Z

Z J ZBZ

Z Z Z Z

Z Z Z ZR

All squares controlled

Later proved impossible with bishops on squares of op-

posite colors. Then the maximum is 63 squares (144 so-

lutions up to symmetry).

2

Maximum (known) number of checkmates in one move:

H. Pollmacher and ve others, 1859

Z ZNZrZ

O ZPJ ZP

Z Z Z Z

ZPZkAQZ

ZRZ Z Z

ZBZNZ Z

Z ZPZ Z

Z ZRZ Z

47 mates in one move

3

Maximum number of forced checkmates in one move:

H. H. Cross, 1936

Z Z Z Z

ZbZ Z Z

pZNZ Z Z

O s Z Z

PZ ZKOrZ

LBj MRO

PZ S O Z

Z Z A Z

29 forced mates in one move

4

The ultimate no-brainer:

Noam Elkies, 1994

KAkZ Z Z

O O Z Zp

ZPo Z O

O Z Z Zp

ZpZ ZrO

Z O Z oB

Z Z ZPZ

Z Z Z Z

Mate in 7

Can the number 7 be increased without promoted pieces

on the board? With promoted pieces a mate in 10 is

possible (Elkies).

5

Ultimate mutual Zugzwang:

H. Hunerkopf, 1972

KAQZ Z Z

oPO Z Z

qj o Z Z

apZPZ Z

o O Z Z

ZPZ Z Z

Z Z Z Z

Z Z Z Z

Whoever moves must be mated in one

Can the number 12 of White and Black initial moves be

increased?

Open. For what (m;n) does there exist a legal position

such that if White moves rst then Blackmust checkmate

White in exactly m moves, while if Black moves rst

then White must checkmate Black in exactly n moves.

(Known only for m = n = 1, and for m = n = 2 using

promoted pieces (Elkies).)

6

Synthetic games.

Shortest game ending ending in checkmate (Fool's Mate):

eight \essentially equivalent" solutions in 2.0 moves (i.e.,

two White and two Black moves). Two solutions have

the nal position:

rmbZkans

opopZpop

Z ZpZ Z

Z Z Z Z

Z Z ZPl

Z Z ZPZ

POPOPZ O

SNAQJBMR

Fool's Mate

7

Shortest game ending with checkmate by capture: 2.5

moves (two essentially equivalent solutions).

rmbl ans

opopjpop

Z Z Z Z

Z Z L Z

Z Z Z Z

Z Z O Z

POPO OPO

SNA JBMR

Mate by capture

8

Construct a legal game of chess in which Black mates

White by discovered check on Black's fourth move.

Construct a legal game of chess in which Black makes

no captures and Black stalemates White on Black's

twelfth move.

Construct a legal game of chess in which Black mates

White on Black's fth move by promoting a pawn to

a bishop.

Construct a legal game of chess in which Black mates

White on Black's fth move by promoting a pawn to

a knight.

9

Length records.

Let n be the largest integer for which there exists a dual-

free mate in n, i.e, in a legal position White is to check-

mate Black in n move. At least one Black defense forces

each White move uniquely. All claims to records derive

from:

W. Jrgensen, 1976

Z Z ZnZ

o ANZ Zb

pZpZ Zno

o o Z oq

Z Z Zks

J O ZrZp

ZPOQZ Z

Z Z Z Z

Mate in 200

Longest one with no doubt about soundness: mate in 208

by A. Cheron (1979). A mate in 226 by Jrgensen himself

may be sound.

See Appendix for solution to above problem.

10

What about mate in n allowing duals (i.e., at least one

Black defense requires n moves by White, but they don't

have to be uniquely determined)? Without promoted

force, the record for a long time was n = 257, by O.

T. Blathy (1889). Recently Ken Thompson reported the

unique longest mate with RN vs. NN.

Ken Thompson (& computer), 1999 or 2000

M Z Z Z

ZRJ Z Z

Z Z m Z

Z Z Z Z

Z Z Z Z

Z Z Z Z

Z Z m Z

Z Z Z j

Mate in 262

This can be extended to at least mate in 265 with a

prequel.

Conclusion: Human beings will never be able to un-

derstand chess completely.

11

Longest dual-free mate where White has only a queen,

based on mate in 127 by O. T. Blathy.

J. Halumbirek (after O. T. Blathy), 1955

Z Z Z Z

o Z Z Zp

Z Z Z o

o Z Z Zp

bZ L Z o

J Z Z Zp

pZrZ Z Z

skZ ZnZn

Mate in 130

Other dual-free mate records:

rook minimal: 69 moves

bishop minimal: 38 moves

knight minimal: 42 moves

pawn minimal: 72 moves

12

ENUMERATIVE PROBLEMS

Let P be a chess position. Let f(n) be the number of dif-

ferent games (or games ending in checkmate, or \games"

where only White moves, etc.) starting from P (with

or without specifying who moves rst). Transfer-matrix

method )

Theorem. Let F (x) =

P

1

n=0

f(n)x

n

. Then F (x) is

a rational function (quotient of two polynomials).

13

Example (Elkies). In the following position, let f(n)

be the number of ways Black can make n consecutive

moves, followed by a checkmate in one move by White.

(Black may not move into check.)

Z Z ZQZ

Z Z Z Zp

Z Z Z j

Z Z Z Z

Z Z Z Z

Z Z Z Z

Z Z Z Z

Z Z Z ZK

Serieshelpmate in n: how many solutions?

Then

1

X

n=0

f(n)x

n

=

x

5

(2 + 5x 4x

2

2x

3

)

(1 x

2

)(1 2x

2

)(1 3x

2

+ x

4

)

= 2x

5

+ 5x

6

+ 8x

7

+ 28x

8

+ 24x

9

+ 108x

10

+ 66x

11

+

f(2m) = 3 2

m+2

+ F

2m+3

; m > 0

f(2m + 1) = 2(F

2m1

1);

where F

n

is a Fibonacci number:

F

1

= F

2

= 1; F

n+1

= F

n

+ F

n1

:

14

Let P be the initial position. Let f(n) be the number of

games in n single moves, and g(n) the number ending in

checkmate. Then

(f(0); f(1); : : : ; f(8)) = (1; 20; 400; 8902; 197281; 4865609;

119060324; 3195901860;

84998978956; 2439530234167):

(g(4); g(5); g(6)) = (8; 347; 10828);

the latter computed in 1897.

15

Classical ballot problem. Let C

n

be the number of

ways 2n voters can vote sequentially for two candidates

A and B, so that each receives n votes and A never trails

B during the voting. E.g., C

3

= 5:

AAABBB AABABB AABBAA ABAABB ABABAB:

C

n

is the Catalan number

C

n

=

1

n + 1

2n

n

:

For 66 combinatorial interpretations, see Exercise 6.19 of

R. Stanley, Enumerative Combinatorics, vol. 2.

16

K. Vaisanen, 1992

Z Z ZkZ

o Z Z Z

pZ ZPO Z

Z Z Z Z

Z Z Z Z

Z Z Z ZK

A Z Z Z

Z Z Z Z

Serieshelpmate in 19: how many solutions?

Serieshelpmate in n: Black moves rst and makes n

consecutive move. White then checkmates Black in one

move. Black and White are cooperating. Black may not

move into check or check White (except possibly on his

last move).

17

ss

s

s

s

s

s

s

s

s

s

s

s

s

s

s

s

s

s

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@

@@

P

1

a5

P

1

a4

P

2

a5

P

1

a3

P

1

a2

P

1

a1N

N

1

b3

N

1

c5

N

1

d7

N

1

f8

N

1

h7

P

2

a4

P

2

a3

P

2

a2

P

2

a1N

N

2

b3

N

2

c5

N

2

d7

N

2

f8

Figure 1: Solution poset

Number of solutions = C

9

=

1

10

18

9

= 4862.

18

RETROGRADE ANALYSIS

R. Smullyan, 1979

Z ZkZ Z

Z Z Z Z

Z Z Z Z

Z Z Z Z

Z Z Z Z

Z Z Z Z

Z O O Z

Z Z J Z

Monochrome chess. A White bishop stands at e3 or e4. Which?

Monochrome chess: every move is to a square of the

same color (so e.g. knights never move).

19

N. Hoeg, 1916

Z Z Z Z

Z ZKZ Z

Z ZPj Z

Z Z Z Z

Z Z Z Z

Z Z Z Z

Z Z Z Z

A Z Z Z

What was the last move?

20

N. Petrovic, 1954

Z Z ZKZ

Z Z Z ZB

Z ZPj Z

Z Z Z Z

Z Z ZQZ

Z Z L Z

Z Z Z Z

A Z Z Z

The last six single moves?

21

J. Furman, 1973

ZBZ Z Z

orZpOpo

kZ Z ZpZ

O Z LpZ

Ko Z Z Z

ZrO Z ZP

POpZPZ O

S Z M ZR

White's Rooks have exchanged places

22

G. Schweig, 1938

rZblkans

opo Zpop

Z o Z Z

Z Z Z Z

Z Z Z Z

Z Z Z Z

POPOPOPO

S AQJBMR

Position after the 4th move of Black. How did the game go?

I.e., proof game in 4.0 moves

23

Phoenix theme:

R. Muller, 1985

mblkans

o o opop

Z o Z Z

Z Z Z Z

Z Z Z Z

Z Z Z Z

OPO OPO

SNAQJBMR

Proof game in 6.5 moves

24

Tibor Orban, 1976

rmblkans

opZ Zpop

ZpZpZ Z

Z Z Z Z

Z ZPZ Z

Z Z Z Z

POPO OPO

SNAQJ MR

Proof game in exactly 4.0 moves

Solution in 3.5 moves is easy!

25

G. Donati, 1998

rm Z Z Z

opZpopo

oqj m o

Z Z Z Z

Z Z Z Z

Z Z Z Z

PO OPOPO

SNAQJBMR

Proof game in 13.5 moves

A nice puzzle!

26

APPENDIX

Solution to mate in 200 by Jrgensen: We sketch the solution to this complex

problem following C. J. Morse. Ample study is necessary for full apprecia-

tion. Certain maneuvers are used repeatedly and are indicated after their

rst appearance by ellipses (: : :). The solution begins 1. Qe6+ Rf5 2. Bh2.

Suppose that White's king were now at d1 and that the ve Black queenside

pawns had no moves. If Black plays Kf3, then Qe2 is mate. The only alter-

native for Black is to move one of his knights. If he moves the knight on g6,

then Ne5 is mate. If Black instead moves the knight on g8, then White mates

in two by Nf6+ Kf3, Qe2 mate. Hence White's goal is to manuever his king

to d1 while capturing or immobilizing Black's queenside pawns. However,

White may not move his king to the fourth rank, since then Black can move

his king o the fourth rank with discovered check. The solution continues

2: : : Kf3 (other moves shorten the solution) 3. Qe3+ (not 3. Qxf5+ Kg2!,

and Black can free his queen. It is essential to keep Black's pieces bottled

up.) Kg2 (of course not Kg4 4. Qg3 mate) 4. Qg1+ Kf3 5. Qf1+ Kg4 (not

Ke4 6. Qd3 mate) 6. Qe2+ Rf3 7. Qe6+ Rf5 8. Ka2 (not 8. Ka4 Kf3+! nor

8. c4 Kf3 leading to 12. Qe2+ Rf3+!) Kf3 : : : 14. Kc1 Kf3 : : : 20. Kd1 a4

(not Kf3 21. Ke2 mate, nor c4 which allows 21. Ke1 a4 22. Kd1) 21. Kc1

(not 21. Ke1 a3!, and Black will be able to queen his pawn and check White

before White can play Ke4 followed by either Qxf5 mate or by mating with

the knight if Black moves a knight) Kf3 : : : 27. Kd1 a5 (c4 is playable here

and at similar positions up to move 92, but not a3 which allows 65. Ke1) 28.

Kc1 Kf3 : : : 34. Kd1 a6 (here a3 is an alternative as well as c4) 35. Kc1 Kf3

: : : 41. Kd1 a3 42. Kc1 Kf3 : : : 48. Kb1 (not 48. Kd1 a2!) Kf3 : : : 54. Ka2 Kf3

: : : 60. Kxa3 Kf3 : : : 66. Kb2 Kf3 : : : 72. Kc1 Kf3 : : : 78. Kd1 a4 : : : 85. Kd1

a5 : : : 92. Kd1 c4 93. Kc1 Kf3 : : : 96. Qf1+ Kg4 (not Ke4 97. e3+ Kd5 98.

Qxf5+ leading to short mate) : : : 99. Kd1 c5 : : : 106. Kd1 a3 107. Kc1 Kf3

: : : 113. Kb1 Kf3 : : : 116. Qf1+ Ke4 (this can be played without shortening

the solution when the White king is not guarding d2) 117. Qxc4+ (not 117.

d3+ Ke3 118. Bg1+ Kd2!) Kf3 118. Qf1+ Kg4 : : : 120. Qe6+ Rf5 121 Ka2

Kf3 : : : 127. Kxa3 Kf3 : : : 145. Kd1 a4 : : : 152. Kd1 c4 : : : 159. Kd1 (not

159. Kb2, leading to 168. Qf1+ Ke4 and 173. Kxa4 Kf3+!) a3 160. Kc1 Kf3

: : : 166. Kb1 Kf3 : : : 169. Qf1+ Ke4 (this can be delayed until move 187) : : :

174. Ka2 Kf3 : : : 180. Kxa3 Kf3 : : : 198. Kd1 (nally reaching the desired

position!) Ng8 moves 199. Nf6+ Kf3 200. Qe2 mate!

27